In aluminum matrix composites, a nonmetallic material, such as ceramic, which is a reinforcing material, is distributed in a matrix formed of pure aluminum or aluminum alloy. Aluminum matrix composites are light-weight, have high strength and rigidity, excellent wear-resistance, and excellent high-temperature characteristics. Due to such characteristics, aluminum matrix composites are expected for use as a structural material for transportation equipment, a material for the mechanical industry, or an electric and electronic material. Mechanical properties of metal matrix composites are heavily dependent upon the kind, size, shape, volume fraction of a reinforcing material to be added, and interface characteristics of a matrix and the reinforcing material. When a ceramic reinforcing material is added into a matrix metal in a liquid phase to prepare a composite material, due to low wetting properties between the ceramic reinforcing material and the matrix metal, it is difficult to provide the ceramic reinforcing material into a molten metal and also, an unwanted interface reaction may occur at the interface between the matrix metal and the reinforcing material to result in a low interface binding force between the matrix metal and the reinforcing material, thereby leading to a decrease in mechanical characteristics of the composite material. To overcome such problems, recently, research into a process, in which a reinforcing phase spontaneously forms inside molten metal, is actively carried out. A reinforcing phase that spontaneously generates in molten metal is thermodynamically stable, and the interface between the reinforcing phase and a matrix is smooth and thus, the interface binding force between the matrix and the reinforcing phase is strong. Accordingly, mechanical properties of a metal matrix composite prepared by using a spontaneous reaction has better mechanical properties than a composite prepared by using a process including supplying a reinforcing material from the outside.
For use as a reinforcing material, titanium carbide (TiC), titanium boride (TiB2), alumina (Al2O3), or the like may be used. Such materials have high hardness and elastic modulus and excellent high-temperature characteristics, and thus, when they are used as a reinforcing phase in an aluminum alloy, the strength, rigidity, high-temperature strength, wear-resistance, or the like of the aluminum alloy may be substantially increased. Due to such characteristics, many trials have been made to form such materials due to a spontaneous reaction.